Projection lens of high numerical aperture

ABSTRACT

A reversed telephoto projection lens of 200x magnification having a numerical aperture of 0.45 and long back focus comprises two groups, a three-element negative group spaced from a sevenelement positive group by a factor of substantially 6.5x the focal length of the lens, being intended for use in a system with a plano-parallel cover glass.

Umtea:

Trotta PROJECTION LENS OF HIGH NUMERICAL APERTURE Filed: Oct. 1, I970[is] 3,656,839 [451 Apr. 18,1972

Primary Examiner-John K. Corbin Attorney-Frank C. Parker ABSTRACT Areversed telephoto projection lens of 200x magnification having anumerical aperture of 0.45 and long back focus comprises two groups, athree-element negative group spaced from a seven-element positive groupby a factor of substan- [21] Appl. No.: 77,271 tially 6.5x the focallength of the lens, being intended for use 7 l 52] in a system with apiano-parallel cover glass. [56] References Cited UNITED STATES PATENTSI 4 Claims, 1 Drawing Figure 3,551,031 12/1970 Grey ..350/2l4 ll IMAGEPLANE PATENTEDAPR 18 I972 3.6 56,83 9

s,, v PATRICK A..TROTTA.

I INVENTOR.

BY IMAGE PLANE ATTORNEY BACKGROUND OF THE INVENTION 1. Field of theInvention My invention lies in the field of optical lenses, and moreparticularly, in the field of multiple component optical lenses.

2. Description of the Prior Art US. Pat. Nos. 3,432,226 and 3,437,403 toThomas S. Bird, and application Ser. No. 838,596, of David S. Grey, nowUS. Pat. No. 3,55 1,031, disclosed earlier inverse telephoto designs ofthe same general kind as the present lens, all of the foregoing beingassigned to the same assignee as the present invention.

It may be noted that the present lens departs from these lenses inincreased nominal magnification and numerical aperture. The negativegroup is more widely separated from the positive group and thesensitivity of the present lens to manufacturing tolerances isminimized. Table I, below, sets forth these comparisons.

TABLE I Ser. No. present 3,432,226 3,437,403 838,596 lens Nominalmagnification l lX 150x [50X 200x Numerical aperture 0.33 0.42 0.42 0.45Separation of lens 3.06F 4.07F 4.97F 6.55F

SUMMARY OF THE INVENTION The lens of my invention is intended to be usedat fixed conjugates with a relatively thick plane-parallel cover glasswhich supports material, as for instance a microfiche card, to beprojected by the lens. The lens is intended to work with the cover glassin the rear conjugate, however, the cover glass is not specified as tothickness or refractive index, since many standard cover glasses arecompatible with the lens, as is more fully discussed below.

The lens has a long back focus, relatively speaking. In addition, itprovides a half-angle field of coverage, good fiatness of field and goodimage resolution. The lens has an extremely high numerical aperture of0.45, which is unusual in a lens having so wide an angle of coverage andbeing so well corrected. The nominal magnification is 200x, however,small variations in the rear conjugates may reduce or increase themagnification by as much as 50X, corresponding adjustment of the imagescreen position being assumed.

The lens comprises two groups of component lenses, with a negative groupcomprising three elements toward the front, or projection side, and apositive group comprising seven elements toward the rear, or objectside, the object here referring to the film gate. The positive group ismade up of three subgroups.

The first subgroup consists of a negative lens which is double concave,and which is air-separated from a thick positive meniscus lens concaveto the rear. The second subgroup begins with a third lens which is arelatively thick double convex lens. It is narrowly air-spaced from thefourth lens which is a negative, double concave lens whose radii are notradically different from its neighboring radii in the third and fifthelements, leading to speculation that a variant of the present lens,suitably designed, oould employ in place of the second subgroup acemented triplet, or possibly even a doublet. The fifth element isair-spaced from the fourth and is a relatively thick double convex lens.The third and last subgroup of the positive lens group begins with arelatively thick sixth element, a double convex lens, air-spaced fromthe fifth element, and ends with a seventh element, a negative meniscuslens concave to ments are both relatively strong negative meniscuslenses,

concave to the rear and being separated by a short airspace, the ninthelement being of larger diameter than the eighth. The 10th element, thelast of both the negative group and of the overall lens, is the largestdiameter single element in the lens. It is spaced relatively widely fromthe ninth element, and it comprises a positive meniscus lens, which is,like all the other meniscus lenses, concave to the rear.

It is an important feature of the lens that it is highly corrected toproduce an image of excellent quality at 200x magnification, thecorrections for spherical aberration and coma being introduced primarilyin the positive group while the corrections for distortion andastigmatism are accomplished primarily in the negative group.

BRIEF DESCRIPTION OF THE DRAWING The drawing depicts a schematic diagramof the lens of my invention.

the rear, and air-spaced from the sixth. As with the second subgroup, adoublet could replace the third subgroup, assuming suitable redesign.

A long space, on the order of 6.5 times the focal length of the entirelens, intervenes between the seventh element of the positive group andthe first element of the negative group, being the eighth elementoverall. The eighth and ninth ele- DESCRIPTION OF THE PREFERREDEMBODIMENT In the drawing my lens appears generally under the bracket10, and it may be seen to include both the positive group 11 and thenegative group 12.

The overall lens is intended to be used with a plane parallel coverglass in the rear conjugate, which is not assigned a Roman Numeraldesignation and is not regarded as one of the lens elements.

The cover glass to be used with my lens may be any of several possibleones. Suppose t is the thickness of the cover glass for which my lenswas specifically designed, being 0.704F, where F is the Focal length ofthe lens. Then if t,, is the thickness of a substituted cover glass, N,is the refractive index of the present cover glass (actually 1.523), andN, is the refractive index of the substituted cover glass, then thesubstituted cover glass must obey the law that to the Third orderapproximation, the tolerance pression being such that on this exshouldvary less than 20.1.

In addition, as respects the Abbe number of the substituted cover glass,11,, and the original, 1 (actually 58.6), the condition is that and thetolerance is that The sequence of lens elements proceeds from back tofront as described above in the summary. The designations thereemployed, i.e., first element, second element," etc., are carriedthrough by labeling the first element, lens Roman Numetal I, and thesecond, lens Roman Numeral Il, etc.

As respects the particular lens elements I to X their equivalent focallengths, respectively, are designated F F etc., referring to the ratiothey bear to the overall lens system focal length, and are given inTable II herebelow. It may be noted that a minus sign is employedtherein to designate negative focal lengths.

TABLE I] -F, I 4.354 F F I 3.865 F Flu I 3478 F -F,,- I 3.191 F F,- I2.998 F F,-, I 6.394 F -F,; I 6.227 F F, I 11.806 F Due to the method ofmanufacture and assembly used for the lens 10, all of the above nominalvalues may in practice be varied by a small amount from the nominal orideal values as given in the foregoing or succeeding tables. In theaforesaid method, comparatively large numbers of each lens element inthe lens are produced according to good manufacturing standards havingpractical limits suitable for large scale production. The resultantnon-ideal lens parts depart slightly from the true nominal values asgiven in the specification and are evaluated as indicated in certain ofthe-tables appearing hereinafter. Particularly the airspaces and lensthicknesses may be adjusted slightly by a skilled optician in such a wayas to restore good optical performance. With a multiplicity of lensparts having varying lens parameters available to skilled operators, itis therefore possible to successfully assemble a large proportion ofnon-ideal lenses which perform well optically and are commerciallyacceptable.

The nominal values for the successive lens radii are given in Table 111below in terms of the numerical ratios of their absolute values, theminus signs used with various radii signifying those lens surfaces whichare concave toward the object.

(Absolute Value) The said radii are further given in Tables 1V and V,below, in terms of their relation to the overall focal length F of thelens, the minus sign again referring to those lens surfaces which areconcave to the object side. Table IV provides the nominal relations ofeach radius, while Table V gives the ranges of the permissiblemanufacturing variations above referred to.

TABLE IV R, 7.O22 F R, 5.760F R, 13.055 F -R, 2.283F R, 19.763 F -12.2.695F R, 4.474F R, 4.878F a, 5.4561

The nominal values and their ranges, respectively, in terms of the focallength F of the overall lens, are given in Tables V1 and VII, below, forthe spaces S, to 8,, between the elements and their thicknesses 2,through t,,. It will be appreciated that the values appearing for S, and2,, relating to the cover glass and its separation from the lens properare only nominal and that certain variations may be allowed in them.Accordingly,

ranges are not given for S, and 1, since these may be determined byroutine trial and error during the mounting of my lens in asuitableinstrument.

TABLE v1 The nominal values and pennissible ranges, respectively of therefractive indices, n and of the Abbe numbers v are given in Tables V111and 1X, below. It may be observed that only three optical glasses,having high, moderate and low refractive indices were employed indesigning my lens.

I claim:

1. in an inverse telephoto lens, for use with a cover glass in the rearconjugate, comprising a rear positive group consisting of threesubgroups of elements wherein:

l. the first subgroup consists of a double concave negative singlet ofhigh refractive index and a relatively thick positive meniscus singletof moderate refractive index;

2. the. second subgroup consists of a positive compound member composedof high and moderate refractive index elements; and

3. the third subgroup consists of a positive compound member composed ofhigh and moderate refractive index elements, an improved front negativegroup consisting of three mutually air-spaced elements wherein:

l. the first is a negative meniscus singlet, concave to the rear;

2. the second is a negative meniscus singlet, concave to the rear; and 13. the third is a positive meniscus singlet concave to the rear, andsaid front negative group is separated from said rear positive group bya factor of at least 6.5 times the overall focal length F of said lens;

said front negative group substantially conforming to the followingcharacteristics wherein the specific lenses, radii, thicknesses andspaces correspond to those described in the foregoing drawing andspecification:

Hpuvos wherein F is the overall focal length of the lens, F is theeffective focal length of each element of said lens (the minus signdenoting negative focal length) in terms of F, and R is a radius (theminus sign denoting concavity to the rear).

3. A lens of the inverse telephoto type for finite conjugates and havinga magnification in excess of lSOX, a numerical aperture of substantially.45, a field half-angle of substantially 20 with excellent resolutionand a' very flat field, said lens comprising in sequence along anoptical axis from an object space located on the surface of a cgyerglass, said cover glass occupying a portion of the rear conjugate ofsaid lens:

a. a negative double concave lens element designated 7 l air-spaced fromsaid cover glass; Y

b. a positive meniscus lens element designated ll, concave toward saidobject space and air-spaced from said lens I;

c. a double convex lens element designated HI and airspaced from saidlens ll; 1 l

d. a negative double concave lens element designated W and air-spacedfrom said lens III;

e. a double convex lens element designated V air-spacedfrom said lensIV;

f. a double convex lens element designated Vl air-spaced from said lensV;

g. a negative meniscus lens element designated Vll. concave toward theobject space and air-spaced from said lens Vl. said lens elements l-Vlltogether comprising a rearward positive lens portion of said inversetelephoto lens; i

h. a negative meniscus lens element designated Vlll, concave toward therear and being air-separated from said lens VII by a length greater than6.5X the the focal length of the overall lens;

. a negative meniscus lens element designated IX, concave toward therear. and being air-separated from said lens VIII; I

'. a positive meniscus lens element designated X, concave toward therear and being air-separated from said lens lX, said lenses Vlll, IX andX forming a frontward negative lens portion of said inverse telephotolens. the nominal equivalent focal lengths of said lens elements l-Xbeing given herebelow in terms of F. the minus sign referring tonegative focal length:

2. An inverse telephoto lens of 10 airspaced elements, for

use with a cover glass in the rear conjugate, having substantially thefollowing characteristics:

the lens elements l, W, VII and) being of glass having substantially,refractive index [.720 and Abbe number 29.3, the lens elements ll, lll,V and VI being of glass having substantially refi'active index 1.691 andAbbe number 54.8, the lens elements VIII and IX being of glass having 4.The lens of claim 3 having successive radii, beginning with said element1, within the ranges listed herebelow:

substantially refractive index 1.516 and Abbe number

1. In an inverse telephoto lens, for use with a cover glass in the rearconjugate, comprising a rear positive group consisting of threesubgroups of elements wherein:
 1. the first subgroup consists of adouble concave negative singlet of high refractive index and arelatively thick positive meniscus singlet of moderate refractive index;2. the second subgroup consists of a positive compound member composedof high and moderate refractive index elements; and
 3. the thirdsubgroup consists of a positive compound member composed of high andmoderate refractive index elements, an improved front negative groupconsisting of three mutually airspaced elements wherein:
 1. the first isa negative meniscus singlet, concave to the rear;
 2. the second is anegative meniscus singlet, concave to the rear; and
 3. the third is apositive meniscus singlet concave to the rear, and said front negativegroup is separated from said rear positive group by a factor of at least6.5 times the overall focal length F of said lens; said front negativegroup substantially conforming to the following characteristics whereinthe specific lenses, radii, thicknesses and spaces correspond to thosedescribed in the foregoing drawing and specification: 10
 2. the secondsubgroup consists of a positive compound member composed of high andmoderate refractive index elements; and
 2. the second is a negativemeniscus singlet, concave to the rear; and
 2. An inverse telephoto lensof 10 airspaced elements, for use with a cover glass in the rearconjugate, having substantially the following characteristics: 15wherein F is the overall focal length of the lens, Fe is the effectivefocal length of each element of said lens (the minus sign (-) denotingnegative focal length) in terms of F, and R is a radius (the minus sign(-) denoting concavity to the rear).
 3. A lens of the inverse telephototype for finite conjugates and having a magnification in excess of 150 X, a numerical aperture of substantially 0.45, a field half-angle ofsubstantially 20* with excellent resolution and a very flat field, saidlens comprising in sequence along an optical axis from an object spacelocated on the surface of a cover glass, said cover glass occupying aportion of the rear Conjugate of said lens: a. a negative double concavelens element designated I air-spaced from said cover glass; b. apositive meniscus lens element designated II, concave toward said objectspace and air-spaced from said lens I; c. a double convex lens elementdesignated III and air-spaced from said lens II; d. a negative doubleconcave lens element designated IV and air-spaced from said lens III; e.a double convex lens element designated V air-spaced from said lens IV;f. a double convex lens element designated VI air-spaced from said lensV; g. a negative meniscus lens element designated VII, concave towardthe object space and air-spaced from said lens VI, said lens elementsI-VII together comprising a rearward positive lens portion of saidinverse telephoto lens; h. a negative meniscus lens element designatedVIII, concave toward the rear and being air-separated from said lens VIIby a length greater than 6.5 X the focal length of the overall lens; i.a negative meniscus lens element designated IX, concave toward the rear,and being air-separated from said lens VIII; j. a positive meniscus lenselement designated X, concave toward the rear and being air-separatedfrom said lens IX, said lenses VIII, IX and X forming a frontwardnegative lens portion of said inverse telephoto lens, the nominalequivalent focal lengths of said lens elements I-X being given herebelowin terms of F, the minus sign (-) referring to negative focal length:-FI 4.354 F FII 3.865 F FIII 3.478 F -FIV 3.191 F FV 2.998 F FVI 6.394 F-FVII 7.663 F -FVIII 5.271 F -FIX 6.227 F FX 11.806 F, the lens elementsI, IV, VII and X being of glass having substantially refractive index1.720 and Abbe number 29.3, the lens elements II, III, V and VI being ofglass having substantially refractive index 1.691 and Abbe number 54.8,the lens elements VIII and IX being of glass having substantiallyrefractive index 1.516 and Abbe number 64.0, the lens elements havingconsecutive spaces S2 to S10 beginning, respectively, with space S2between said lens elements I and II, and said lens elements havingconsecutive thicknesses t2 to t11, said thickness t2 referring to saidlens element I, said spaces and thicknesses being set forth inpermissible ranges herebelow: 0.095 F<S2<0.142 F 0.279 F<t2<0.289 F0.009 F<S3<0.013 F 0.943 F<t3<0.952 F 0.043 F<S4<0.052 F 0.727F<t4<0.741 F 0.107 F<S5<0.112 F 0.348 F<t5<0.362 F 0.013 F<S6<0.017 F0.895 F<t6<0.905 F 0.175 F<S7<0.180 F 0.585 F<t7<0.599 F 6.531F<S8<6.578 F 0.320 F<t8<0.343 F 0.403 F<S9<0.426 F 0.272 F<t9<0.296 F0.671 F<S10<0.695 F 0.272 F<t10<0.296 F 171.00 F<S11<210 F 0.674F<t11<0.679 F.
 3. the third is a positive meniscus singlet concave tothe rear, and said front negative group is separated from said rearpositive group by a factor of at least 6.5 times the overall focallength F of said lens; said front negative group substantiallyconforming to the following characteristics wherein the specific lenses,radii, thicknesses and spaces correspond to those described in theforegoing drawing and specification: 10
 3. the third subgroup consistsof a positive compound member composed of high and moderate refractiveindex elements, an improved front negative group consisting of threemutually air-spaced elements wherein:
 4. The lens of claim 3 havingsuccessive radii, beginning with said element I, within the rangeslisted herebelow: 6.889 F<-R1<7.155 F 5.685 F<R2<5.835 F 12.735F<-R3<13.375 F 2.278 F<-R4<2.288 F 19.396 F<R5<20.130 F 2.690F<-R6<2.700 F 4.457 F<-R7<4.491 F 4.859 F<R8<4.897 F 5.433 F<R9<5.479 F3.106 F<-R10<3.118 F 6.052 F<R11<6.118 F 15.242 F<-R12<15.744 F 4.619F<-R13<4.663 F 29.073 F<-R14<31.105 F 1.825 F<-R15<1.831 F 5.835F<-R16<5.903 F 1.656 F<-R17<1.660 F 3.617 F<-R18<3.633 F 56.833F<-R19<59.131 F 7.440 F<-R20<7.472 F